FA551x ETC, FA551x Datasheet - Page 14

• Manufacturer Part Number: FA551x
• Description: CMOS IC For Switching Power Supply Control
• Manufacturer: ETC

FA551X
1. Deciding the startup circuit
These ICs, which use CMOS process, consume less current,
and therefore can use larger startup resistance than the
conventional bipolar type of IC. To decide the startup
resistance, the following conditions must be satisfied:
(a) The IC is started when the power is turned on.
(b) The IC consumption current is supplied during latch mode
(c) The IC consumption current is supplied during the off state
However, these are the minimum conditions for using the IC.
The startup time required for the power supply must also be
decided on.
1.1 Connecting the startup resistor before rectification
When the startup resistor is connected before rectification (AC
line) as shown in Figure 18, the voltage applied to the startup
resistor forms a half-wave rectified waveform of the AC input
voltage. Startup resistor R1 must satisfy the three equations
shown below. Select a smaller-side value for R1 in
consideration of the temperature characteristics.
(a) To supply startup current 30µA at ON threshold voltage
(b) To supply IC consumption current 80µA (max.) (Vcc=10V) in
R1
(c) To supply IC consumption current 200µA (max.) (Vcc=17V)
R1
R1: Startup resistance [k ]
Vac: Effective value of AC input voltage [V]
If neither the latch mode operation nor the on/off functions are
used, only the expression in (5) needs to be satisfied. In this
method, the supply current to the IC via the start-up resistor is
stopped when AC input is shut down. Therefore, after latch
mode operation, shutting the AC input down resets the latch
mode in a very short period of time.
14
R1
operation to maintain the latch state.
under the on/off function to maintain the off state.
17.5V (max.) of UVLO:
latch mode:
in the off state under the on/off function:
Design advice
(AC line)
2
2
2
0.08
Vac – 10
Vac – 17
0.2
Vac – 17.5
0.03
........................................................ (6)
........................................................ (7)
...................................................... (5)
AC INPUT
Fig. 18
FA551X
VCC
R1
DB
~
~
Startup circuit (1)
+
6
5
OUT
C1
C2
D1
MOSFET
Rs
T1